X100 F4.0 sharper than F8.0?
If you would check out a bunch of lens tests—here or on Photozone.de—you will see that the sweet spot for most lenses in the f/1.8-2.0 range tends to be around f/4.0-5.6 and down just a tad by f/8.0. Your mileage may vary a bit from lens to lens.
|Fangorn Forest by cand1d|
|Yosemite Falls with Moonbow by Jonathan Shapiro|
from Best Landscape of the Week 4